Recently, apparatus utilizing or consuming a liquid, e.g., inkjet recording apparatus which form an image on a recording medium by applying an ink that is a liquid onto the recording medium using an inkjet recording head are widely used for printing operations including color printing because they make relatively low noises during printing and they are capable of forming small dots with a high density. One type of such inkjet recording apparatus has an inkjet recording head that is supplied with an ink from an ink tank integrally or separably attached thereto, a carriage that carries the recording head and scans the recording head relative to a recording medium in a predetermined direction, and transport means that transports the recording medium relative to the recording head in a direction orthogonal to the predetermined direction (sub-scanning), the apparatus performing recording by ejecting the ink during main scanning of the recording head. In some apparatus, are cording head capable of ejecting a black ink and color inks such as yellow, cyan, and magenta inks is mounted on a carriage to allow not only monochromatic printing of text images using the black ink but also full-color printing through changing of an ejecting ratio among the inks.
In such inkjet recording apparatus, it is important to discharge a gas such as air which is about to enter or has entered an ink supply channel properly.
Gases that can enter a supply system are generally categorized into four types according to factors generating them as follows:
(1) gasses that enter through ink ejection openings or orifices of a print head or gasses generated as a result of an ejecting operation
(2) products of separation of gasses that have dissolved in ink
(3) gasses that enter a supply channel as a result of gas transmission through the material of which the supply channel is made up
(4) gasses that enter when a cartridge type ink tank is replaced
A liquid path formed in an inkjet recording or print head has a very fine configuration, and ink supplied from an ink tank to the recording head is therefore required to be in a clean condition in which there is no foreign substance such as dust in the ink. Specifically, when foreign substances such as dust have entered, a problem arises in that the foreign substances clog up an ejection opening that is an especially narrow part of an ink channel in the recording head or a part of the liquid path in direct communication with the ejection opening. As a result, an ink ejecting operation can not be performed properly, and the function of the recording head may not be recovered.
Under such circumstances, a configuration is frequently employed in which a filter member for removing foreign substances is provided in an ink supply channel between a recording head and an ink supply needle that is stuck into an ink tank to make it possible to prevent foreign substances from entering the recording head side with the filter member.
Incidentally, there is a recent trend toward greater numbers of ejection openings for ejecting ink in order to achieve recording at higher speeds, and drive signals having higher and higher frequencies are coming into use to be applied to elements for generating energy for ink ejection. This has resulted in an abrupt increase in ink consumption per unit time.
This obviously results in an increase in the amount of ink that passes through a filter member and, in order to reduce pressure loss attributable to a filter member, it is effective to provide a filter member having a large area by enlarging a part of the supply channel. As a result, when bubbles enter the supply channel, they are apt to stay in a space in the enlarged part located upstream of the filter member and will become unremovable, in which state a problem arises in that smooth supply of the ink is hindered. There is another possibility that the gas residing in the supply channel enters the ink led to the ejection opening as microscopic bubbles to cause problems such as disabled ink ejection.
It is therefore strongly desired to remove air residing in an ink supply channel quickly, and there are several solutions to this.
One solution is to perform a cleaning operation as described below.
An inkjet recording head performs printing by ejecting ink that is a liquid, for example, in the form of droplets from an ejection opening that is provided opposite to a recording medium. Therefore, printing may fail for causes such as an increase in ink viscosity or solidification of the ink attributable to evaporation of the ink solvent through the ejection opening, deposition of dust at the ejection opening, and clogging of the ejection opening attributable to invasion of bubbles into a liquid channel inside the ejection opening.
Under such circumstances, an inkjet recording apparatus is equipped with capping means for covering the ejection openings of the recording head during non-printing operations or a wiping member for cleaning the surface of the recording head where the ejection openings are formed (ejection opening forming surface) as occasions demand. The capping means functions not only as a cover for preventing ink at the ejection opening from being dried as described above when printing is ceased. When the ejection opening is clogged, the capping means covers the ejection opening forming surface with a capping member and exerts a negative pressure, for example, with a suction pump that is in communication with the interior of the capping member to evacuate the ink from the ejection opening, the capping means thus providing the function of eliminating any ink ejection failure attributable to clogging due to solidification of the ink at the ejection opening, the ink with increased viscosity in the liquid path, or bubbles contained therein.
A process of discharging ink by force to eliminate such ink ejection failures is referred to as a cleaning operation, and it is performed when printing is resumed after the apparatus has been out of operation for a long time or when a user notices that the quality of recorded images has deteriorated and operates, for example, a cleaning switch. Further, the process is accompanied by an operation of wiping the ejection opening forming surface with a wiping member constituted by an elastic plate made of rubber after evacuating the ink by force as thus described.
There is another approach in which, at the time of initial charging to charge the flow channel or liquid path of a recording head with ink or at the time of a cleaning operation performed when an ink tank is replaced, a suction pump is driven at a high speed to exert a great negative pressure upon the ejection opening forming surface that is capped and in which a high flow rate is achieved in the ink supply channel to discharge bubbles contained therein.
However, when the surface area of a filter member is increased to suppress a dynamic or kinetic pressure of the filter member as described above, the sectional area of the flow channel also increases. As a result, even when a great negative pressure is generated in the flow channel during the cleaning operation as ascribed above, a flow rate that is high enough to transport bubbles effectively will not be generated, and it is quite difficult to remove the entrapped bubbles from the ejection opening side using a suction pump. That is, the ink must be at a predetermined flow rate when passing the filter as a requirement to be satisfied to allow the bubbles to pass the filter as a result of an ink flow caused by the suction pump, and a great pressure difference must be generated across the filter to generate such a flow rate. This is normally achieved by increasing the resistance of the flow channel through a reduction of the filter surface area or increasing the flow volume of the suction pump. However, when the filter is made smaller, its performance of supplying ink to the head is reduced and, when it is attempted to remove a gas using a high flow volume, a great amount of ink is discharged to result in wasteful consumption of the ink.
Thus, there is left two other possible methods of removing bubbles, i.e., a method in which bubbles are directly discharged to the outside and a method in which bubbles are moved to an ink tank and kept in a part of the tank where they do not hinder the supply of ink. The former method involves a configuration in which a hole for communication to the outside is provided in an ink supply channel, and this method is not preferable for the reasons described below.
In most ordinary inkjet recording apparatus, in order to prevent undesirable leakage of ink through an ejection opening, a capillary force generating member such as an absorber is disposed in an ink tank or a negative pressure is generated in an ink containing space in an ink tank by providing an elastic member such as a spring in an flexible ink containing bag to exert an urging force in the direction of increasing the internal volume of the same. In such cases, when a simple communication hole is provided in the supply channel to remove bubbles, since the negative pressure is canceled by invasion of air through the communication hole, it becomes necessary to dispose a pressure-regulating valve at the communication hole. This is not preferable because the structure of the ink supply system and consequently the structure of a recording apparatus utilizing the same become complicated and large-sized. Further, in order to prevent leakage of ink through the communication hole for removing bubbles, it is required to dispose a water repellent film which allows a gas to pass but disallows a liquid to pass or a device for opening the communication hole only when bubbles are contained to discharge the bubbles (a mechanism for detecting the quantity of bubbles or a mechanism for opening and closing the communication hole). This results in an increasing in the manufacturing cost and a complicated and large-sized structure.
The approach of moving bubbles into an ink tank will now be discussed. In dosing so, it is preferable to be able to transport the ink to the head in a quantity equivalent to the volume of the bubbles or gas to be moved into the ink tank because this will keep the internal volume of the ink tank unchanged and keep a negative pressure generated therein constant to allow a negative pressure, which is in equilibrium with the ability of the recording head to hold meniscus formed at the ejection opening, to be applied to the recording head. In the case of a cartridge type ink tank, since it is replaced with new one when the ink contained there is runs out, the ink tank can be regarded as having a configuration which allows a gas to be completely eliminated from the ink supply system.
In popular inkjet recording apparatus for consumers, however, a configuration is frequency employed in which cartridge type ink tanks containing a black ink and color inks, respectively, can be detachably mounted on a recording head or a carriage mounting the head from above the same. Specifically, many of the cartridges are configured so that they are stuck by hollow ink supply needles mounted on the carriage with their points directed upward to allow the inks to be supplied to a recording head. Therefore, attention is to be paid on the inner diameter of the ink supply needles that connect the ink cartridges and the recording head. Specifically, while it is desired to use thin supply needles to allow a cartridge mounting operation to be easily performed without requiring a great force, a reduction in the inner diameter of the needles disallows smooth movement of bubbles because of a corresponding increase in meniscus force.
Several proposals have been made on the mechanism for moving a gas into an ink tank.
For example, in Japanese Patent Application Laid-open No. 5-96744(1993), a configuration is disclosed in which a recording head is separated into a first chamber having an atmosphere communication hole and a second chamber having a capillary force generating member and in which the first chamber and an ink tank are connected through two or more communication channels that open into the first chamber at different elevations to supply air into the ink tank through one of the communication channel. In such a configuration, since a negative pressure is exerted on a print head by a difference between water heads in the first and second chambers or the capillary force generating member provided in the second chamber, the atmosphere communication hole is provided at the first chamber.
However, the configuration of the aforementioned reference is aimed at introducing atmosphere into the ink tank in accordance with the supply of the ink in order to use up the ink in the ink tank that is not deformed and is not aimed at discharging bubbles contained in the ink supply channel into the ink tank. That is, the technique disclosed in this application cannot be used to transport a gas from the ink supply channel especially the second chamber or recording head to the ink tank.
As another proposal, Japanese Patent Application Laid-open No. 11-309876(1999) discloses a configuration in which a gas-preferring introduction channel and a liquid delivery channel are provided at a communication section for connecting a chamber for containing a negative pressure generating member and a liquid containing chamber that are separable from each other to ensure that a gas is introduced into the liquid containing chamber. However, this application also discloses a configuration wherein a capillary force generating member and an atmosphere communication hole are provided between an ink tank and a recording head, the configuration represents an open type ink supply channel to and from which a gas freely enters and exits through an opening as the atmosphere communication hole as seen in Japanese Patent Application Laid-Open No. 5-96744 (1993). The technique discloses in the same application cannot be used to eliminate bubbles entrapped in an ink supply channel.
Further, U.S. Pat. No. 6,347,863 discloses an ink container 50 formed with a drain conduit 66, 72 or 74 and a vent conduit 76, 82 or 84 that protrude from the bottom of the container and describes a configuration in which an upper opening of the drain conduit is located on the bottom of an inner wall of the container and in which an opening of the vent conduit is located in a containing space of the container. The technique disclosed in this document is aimed at configuring a system for refilling a member 14 having a reservoir 16, 18 or 20 with ink and is not aimed at removal of bubbles entrapped in an ink supply channel downstream of the reservoir or in a section that uses the ink. Since lower openings of the drain conduit and the vent conduit are at the same elevation, there is a possibility that movement of a liquid and gas is disabled when meniscuses are formed in the conduits. Further, there is no description of an atmosphere communicating hole in this document, in a state that a system composed of ink container (50) and pressure plates (14) is closed, the inner negative pressure abruptly increases while a continuous use of ink, resulting in a disable supply of the ink to the ink-consuming section. In view of the aforementioned, it is considered the atmosphere communication hole is provided with any part of the system. Considering a disclosure that reservoir (16, 18, 20) is filled with foam (90), and a configuration and functions of the gas-preferring introduction channel, the ink container (50) shown in FIG. 2 of this document and the like, it is assumed that the atmosphere communication hole is placed at a side of the reservoir (16, 18, 20). In any case, there is no perspective that a positive elimination of bubbles remaining in the ink supplying channel is performed due to the above-mentioned 1) to 4).
Further, Japanese Patent Application Laid-open No. 10-29318(1998) discloses a configuration in which a replenishing tank for replenishing a reservoir tank with ink can be coupled to the tank that has a chamber containing a negative pressure generating member and an ink containing chamber and in which, when the replenishing tank is coupled to the ink containing section in an upper part and a lower part of the same, the ink is introduced into the ink containing chamber from the replenishing tank through a liquid communication pipe associated with the lower part, and air is introduced into the replenishing tank from the ink containing chamber through a gas communication pipe associated with the upper part. However, the application is not essentially different from Japanese Patent Application Laid-open No. 5-96744(1993) and Japanese Patent Application Laid-open No. 11-309876(1999) in the configuration in which a negative pressure generating member and an atmosphere communication hole are provided between an ink containing chamber and a recording head. The technique discloses in the same application cannot be used to eliminate bubbles entrapped in an ink supply channel.
Japanese Patent Application Laid-open No. 2001-187459 discloses a configuration as shown in FIG. 23 in which a sub-tank 1022 for replenishing a main tank 1020 in communication with a recording head 1018 with ink is attached to an upper part of the main tank to introduce a gas in the main tank into the sub-tank and to supply the ink in the sub-tank into the main tank through acceleration and deceleration of a carriage. According to the application, the main tank section has means for introducing atmosphere although the main tank section in communication with the sub-tank contains the ink in a free state or directly, which configuration is not essentially different from those in Japanese Patent Application Laid-open Nos. 5-96744(1993), 11-309876(1999), and 10-29318(1998). That is, the proposal lacks the viewpoint of positive elimination of bubbles entrapped in an ink supply channel due to the above (1) to (4).
The configurations in Japanese Patent Application Laid-open Nos. 5-96744(1993), 11-309876(1999), 10-29318(1998), and 2001-187459 are similar in that a separable liquid containing section (ink tank) is in communication with a recording head through a plurality of communication channels and in that atmosphere introducing means is provided downstream of the communication channels (on the recording head side of the channels). Problems with this configuration will be described below with reference to Japanese Patent Application Laid-open No. 2001-187459 as a typical example.
FIG. 23 is a conceptual diagram for explaining the invention disclosed in the Japanese Patent Application Laid-open No. 2001-187459. A discussion will be made on balance among forces acting on the region of a meniscus formed in a pipe 1056A on an assumption that movement of air (movement of air into a sub ink chamber 1081 of a sub tank 1022 through the pipe 1056A) has stopped in the illustrated state. First, there are forces acting downward, i.e., a pressure HA originating from a water head difference between the level of ink in the sub ink chamber 1081 and the position of the meniscus that is formed at an opening of the pipe 1056A and a pressure MA originating from meniscus force. Further, there is a force acting upward, i.e., a pressure P originating from air stored in an ink bag 1100 that is disposed in a main tank 1020. All of those forces or pressure have come to a balance to stop the movement of air. In this case, the pressure P of the air is balanced with a sum of the pressure originating from the water head difference between the level of the ink in the sub ink chamber 1081 and the position of the level of the ink in the ink bag 1100 and the pressure originating from the meniscus force (P=HA+MA). Further, since the ink in the sub ink chamber 1081 and the ink in the ink bag 1100 are in communication with each other, a difference HB−HA between the downward ink pressure acting on the meniscus formed at the pipe 1056A and the pressure of the gas in the ink bag 1100 is equal to the pressure HB−HA originating from the water head difference between the position of the meniscus at the pipe 1056A and the level of the liquid in the ink bag 1100. The balance between the pressure originating from the water head difference HB−HA and meniscus pressure MA has consequently brought about an equilibrium state.
When the level of the liquid in the ink bag 1100 is lowered from the state as a result of introduction of bubbles from a bubble generator 1104 by consumption of ink, the pressure HA−HA originating from the water head difference between the position of the meniscus at the pipe 1056A and the level of the liquid in the ink bag 1100 increases. When the pressure exceeds the meniscus pressure, air is introduced into the sub ink tank 1081, and the ink in the sub ink chamber 1081 is supplied to the ink bag 1100 accordingly.
When the ink is ejected at a recording head 1018, however, since a flow of ink occurs throughout the supply system, a pressure loss in accordance with the ink flow rate or volume in the pipe 1056B occurs between the sub ink chamber 1081 and the ink bag 1100. This results in a need for taking the pressure loss into consideration in reviewing the above-described relationship between the meniscus pressure and the pressure originating from the water head difference between the meniscus position and the level of the liquid in the ink bag 1100. Consequently, movement of air occurs when the pressure originating from the water head difference between the meniscus position and the level of the liquid in the ink bag 1100 is greater than a pressure that is obtained by reflecting the pressure loss in the above-described meniscus pressure. That is, unlike the state in which movement of air has been stopped, no gas-liquid exchange occurs in an ink-ejecting state or a dynamic state unless the liquid level is further lowered in a quantity corresponding to the pressure loss at the pipe 1056B in accordance with the ink flow rate. When the liquid level at which the gas-liquid exchange to be started becomes lower than the opening of the pipe 1056B, no gas-liquid exchange occurs, and the ink in the main tank 1020 is used up with the ink in the sub tank 1022 left unused.
Therefore, when the pipe is made thin to facilitate the tank mounting operation as described above, the pressure loss increases accordingly, and attention must be paid on the fact that the liquid level at which gas-liquid exchange in the main tank is to be started becomes lower accordingly. That is, it becomes inevitable to increase the size of the main tank, which results in an increase in the size of the recording apparatus as a whole.
Another problem with the configuration as shown in FIG. 23 is the fact that the bubble generator 1104 is disposed in a lower part of the ink tank. Specifically, while it is strongly desirable to minimize transportation of bubbles to the ink ejection opening, as an ink ejecting operation proceeds, bubbles introduced from the bubble generator 1104 can be entrained by the flow of ink toward the recording head 1018 to enter a flow channel 1041 in communication with the recording head 1018. Therefore, in order to prevent such entrainment of bubbles, it is necessary to take measures such as limiting the flow of ink accompanying the ink ejecting operation and disposing the bubble generator 1104 in a position apart from a filter section 1039, which results in a further increase in the size of the main tank 1020.
Those problems are similarly encountered in the configurations in Japanese Patent Application Laid-open Nos. 5-96744(1993), 11-309876(1999), and 10-29318(1998) that are configurations including atmosphere introducing means provided on the recording head side of the communication channel.